Wire electrode clamping mechanism of wire-cut electric discharge machine

ABSTRACT

A wire electrode clamping mechanism of a wire-cut electric discharge machine is constituted by a wire guide pipe for guiding the wire electrode; a pipe holder for accommodating the upper portion of the wire guide pipe in such a manner that the wire guide pipe is capable of moving up and down; and a clamping member disposed on an upper portion of the pipe holder and operated by the wire guide pipe for clamping the wire electrode, the clamping member clamping the wire electrode which has been passed through the interior of the wire guide pipe.

DESCRIPTION

1. Technical Field

This invention relates to improvements in a wire electrode clampingmechanism mounted on a wire electrode pull-up mechanism for pulling up asevered wire electrode in a wire-cut electric discharge machine.

2. Background Art

A wire-cut electric discharge machine operates by impressing a pulsedvoltage across a wire electrode and a workpiece to produce an electricaldischarge across the intervening space for the purpose of eroding theworkpiece, and moving the workpiece relative to the wire electrode onthe basis of machining command data to cut the workpiece into anydesired contour. Ordinarily, the workpiece is provided with a holethrough which the wire electrode is passed at the start of cutting. In acase where a plurality of these cutting starting holes are provided, thewire-cut electric discharge machine has an attached automatic wireelectrode connecting device for severing the wire electrode at the endof a job which has started at one of the cutting starting holes, passingthe wire electrode through the next cutting starting hole, tensioningthe wire electrode and carrying out automatic operation. Further, thereare occasions where the wire electrode breaks within the workpiece ifsuch machining cutting conditions as the impressed voltage, wireelectrode feed speed and tension are improper during the electricdischarge operation. In the event of such, breakage of the wireelectrode, it is required that this fact be sensed by a wire breakagesensor provided on the electric discharge machine and that the wireelectrode be restored automatically without delay by an automatic wireelectrode recovery device attached to the wire-cut electric dischargemachine.

FIG. 1 is a view showing the construction of a wire-cut electricdischarge machine having the conventional automatic wire connecting andautomatic recovery devices. In the Figure, numeral 1 denotes a columnand 2 a wire electrode wound around a delivery reel 3 arranged on thecolumn 1. The wire electrode 2 paid out by the delivery reel 3 is passedthrough a hole 21 in a workpiece 12 via a friction brake 4, a roller 5driven by a drive motor 18, a guide roller 6, a lower guide 7, a wireelectrode feed mechanism 9 and a lower nozzle 11. The wire electrode 2is delivered to a wire electrode processing device 17 via a gripper 110of a wire electrode clamping mechanism 30 provided on the distal end ofa wire electrode pull-up mechanism 13, an upper guide 14, a conductionpin 15 and feed rollers 16. A table mechanism 19 on which the workpiece12 is set is adapted to be moved in X and Y directions by two workpiecefeed motors MX, MY, respectively. Numeral 20 denotes a drive motor forthe wire electrode pull-up mechanism 13. By winding up or paying out arope 22, one end of which is fastened to the pull-up mechanism 13, themotor moves the wire electrode pull-up mechanism 13 up and down. L₁denotes a limit switch for sensing breakage of the wire electrode 2, andL₂, L₃ represent limit switches for sensing when lowering and elevationof the wire electrode pull-up mechanism 13 have been completed,respectively. Numeral 8 in the Figure denotes a cutter arranged betweenthe wire electrode feed mechanism 9 and the lower nozzle 11, and numeral10 designates a wire position sensor arranged between the cutter 8 andthe nozzle 11.

In a wire-cut electric discharge machine having the above construction,the wire electrode 2 is guided so as to be oriented substantiallyvertically between the lower guide 7 and the upper guide 14 and ispulled upwardly by the feed roller 16 longitudinally so as to travel bythe portion where the workpiece 12 is cut. A prescribed voltage isimpressed across the wire electrode 2 and the workpiece 12, and thetable mechanism 19 is driven by the workpiece feed motors MX, MY totransport the workpiece 12 in a horizontal plane, whereby electricdischarge machining is performed along a desired contour.

When the wire electrode 2 breaks in passing through the workpiece 12,the limit switch L_(l) for sensing wire breakage is actuated toimmediately halt the electric discharge machining operation.Concurrently, rollers 91, 92 of the wire electrode feed mechanism 9clamp the wire electrode 2 on the lower side of the workpiece 12 to stopthe wire electrode 2 on the supply side from sliding down. Meanwhile,the spent wire electrode 2 which has come free of the workpiece 12 ispulled up by the feed rollers 16 and is fed into the wire electrodeprocessing device 17 where the wire electrode is processed e.g., by itbeing cut up into small pieces. Next, the wire electrode 2 left in theworkpiece 12 is pulled down by the wire electrode feed mechanism 9 andthe distal end portion of the severed wire electrode 2 is pulled out ofthe workpiece 12. Thereafter, the table 19 is moved to return theworkpiece 12 to the position of the cutting starting hole, the wireelectrode pull-up mechanism 13 is lowered toward the workpiece 12 by thedrive motor 20, the gripper 110 at the distal end thereof is broughtinto abutting contact with the workpiece 12, the wire electrode feedmechanism 9 is reactuated to feed the end of the wire electrode 2 intothe cutting starting hole of the workpiece 12, the end of the wireelectrode is fed so that a predetermined length of the wire electrode isprojected from the upper side of the workpiece 12 as the wire electrodeis guided by the lower nozzle 11, and in this way the end of the wireelectrode is inserted into the gripper 110 of the wire electrodeclamping mechanism 30.

Described next will be the gripper 110 of the wire electrode clampingmechanism 30. The conventional gripper 110 is constructed so as tooperate in the manner shown in FIG. 2. Specifically, as shown in FIG.2(a), the end of an operating rod 110d abuts against the upper surfaceof the workpiece 12 as the gripper 110 is lowered in the mannerdescribed above. As the gripper 110 continues to be lowered, theoperating rod 110d pivots in the counter-clockwise direction about apivot shaft 110f, causing a position adjusting screw 110n to abutagainst a clamping member 110c. With further descent of the gripper 110,as shown in FIG. 2(b), the position adjusting screw 110n rotates theclamping member 110c counter-clockwise about a shaft 110q so that a cambody 110h is brought into position above a cam operating body 110p ofthe operating rod 110d. As the gripper 110 continues to be lowered, thecam operating body 110p presses up on the cam body 110h, therebyamplifying the effect of the operating rod 110d to swing the clampingmember 110c about the shaft 110q through a large angle in thecounter-clockwise direction. As a result, the clamping member 110c isrotated counter-clockwise through an angle of about 90 degrees from theposition shown in FIG. 2(a) to the position shown in FIG. 2(c). A coiledspring 110i is twisted and strongly biased while the clamping member110c is being turned. When the lower surface of the operating rod 110comes into intimate abutting contact with the upper surface of theworkpiece 12, the rope 22 actuating the wire electrode pull-up mechanism13 slackens, limit switch L2 opens, and motor 20 is stopped to halt thedescent of the gripper 110.

Next, the wire electrode feed mechanism 9 is actuated to feed the wireelectrode 2 upwardly, whereupon the end of the wire electrode 2 isthreaded through the hole 21 in the workpiece 12 and passed through anozzle 110l of the operating rod 110d, with the wire passing the innerside of a support wall 110j at the end of an arm 110a and emerging fromthe upper side of the arm, as shown in FIG. 2(c). This is followed byrunning the motor 20, shown in FIG. 1, in the reverse direction,whereupon the gripper 110 is raised. Now the operating rod 110d isrotated in the clockwise direction about the pivot shaft 110f owing tothe restoration force of the coiled spring 110i. This motion isamplified and transmitted to the clamping member 110c owing to therelation between the cam operating portion 110p and the cam body 110h.The clamping member 110c rotates through a large angle in the clockwisedirection, which is opposite to the direction mentioned above, about theshaft 110q. This rotating motion results from the restoring force of thecoiled spring 110i. A restraining portion 110g urges the wire electrode2 against the support wall 110j. As the gripper 110 continues to rise,the wire electrode 2 is clamped between the restraining portion 110g andthe support wall 110j. Owing to the wedge effect of the restrainingportion 110g, any attempt by the wire electrode 2 to fall is fullycounteracted by a stronger clamping force. The gripper 110 thus israised while carrying the clamped wire electrode 2 along with it. At theend of the elevating operation, limit switch L3 shown in FIG. 1 isclosed to suspend the rotation of the motor 20. At this time the end ofthe wire electrode 2 has been pulled up to a position high enough topermit it to be clamped by the feed rollers 16, the latter then beingrotated to pull up the wire electrode 2.

The foregoing conventional arrangement has a number of drawbacks. First,if the inner surface of the cutting starting hole 21 in the workpiece 12is very rough, the wire electrode 2 will snag on the inner surface ofthe cutting starting hole 21 or the end of the wire electrode willprotrude from the upper surface of the workpiece 12 upon being bent intothe shape of a hairpin or will form an obstruction within the cuttingstarting hole. In cases such as these the gripper 110 will not be ableto grasp the end of the wire electrode.

Further, if the diameter of the cutting starting hole 21 is larger thanthat of the nozzle 110l of the gripper 110 and smaller than the overallsize of the gripper 110, or if a cut hole in the shape of a slit extendsfrom the cutting starting hole, the end of the wire electrode 2 willmove within the cutting starting hole and not reach the nozzle of thegripper 110, with the result that the latter will not be able to graspthe end of the wire electrode 2. Second, since the amount of verticaltravel of the gripper 110 covers a long distance extending from theworkpiece surface to the feed rollers 16, it is difficult to maintainthe positional accuracy of the nozzle 110l, which is provided on theoperating rod 110d of the gripper 110, with respect to the hole 21 inthe workpiece 12, and to assure the positional accuracy of the wireelectrode 2, which is held by the gripper 110, with respect to the feedrollers 16. As a result, a situation arises wherein the position of thehole 21 in the workpiece 12 and the position of the nozzle 110l of theoperating rod 110d do not coincide, making it impossible for the wireelectrode 2 to be clamped. Third, since the wire electrode 2 iscompletely unguided during movement, the wire becomes unstable and maytwist or break. Fourth, since the clamping member 110c is rotated backand forth by the operating rod 110d, construction is complicated andadjustment difficult.

Accordingly, an object of the present invention is to provide a wireclamping mechanism for a wire-cut electric discharge machine, whichclamping mechanism is capable of guiding the wire electrode reliably andhas a simple construction.

SUMMARY OF THE INVENTION

The present invention provides a wire electrode clamping mechanism for awire-cut electric discharge machine, the clamping mechanism beingmounted on a wire electrode pull-up mechanism, which pulls a wireelectrode up to a position of feed rollers disposed above a workpiece,for clamping the wire electrode delivered by a wire electrode feedmechanism disposed below the workpiece, the wire electrode clampingmechanism comprising a wire guide pipe for guiding the wire electrode, apipe holder for accommodating the upper portion of the wire guide pipein such a manner that the wire guide pipe is capable of moving up anddown, and a clamping member disposed on an upper portion of the pipeholder and operated by the wire guide pipe for clamping the wireelectrode.

Thus, according to the present invention, the wire clamping mechanismhas a wire guide pipe for reliably guiding the wire electrode so thatthe wire electrode can be accurately and postively grapsed and raisedeven if the cutting starting hole has a very rough inner surface or alarge diameter. As the wire electrode is being pulled up, it will notbecome unstable and twist, so that there is no danger of damage to theelectrode. Further, according to the present invention, the wire guidepipe is provided on the lower portion of the clamping member. This makesit possible to shorten the travelling distance for pulling up the wireelectrode, thereby enabling the clamping operation to be performed inreliable fashion. According to the invention, the wire guide pipe isaccommodated by the pipe holder so as to be capable of moving up anddown, and the clamping member is actuated by the vertical motion of thewire guide pipe itself. Accordingly, a complex arrangement for operatingthe clamping member is unnecessary.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side view showing the construction of a wire-cut electricdischarge machine;

FIGS. 2(a), 2(b) and 2(c) are side views for describing a wire electrodeclamping mechanism according to the prior art;

FIGS. 3(a) and 3(b) are views showing the construction of an embodimentof a wire electrode clamping mechanism according to the presentinvention;

FIG. 4 is a partial, cross-sectional view showing the wire electrodeclamping mechanism of the present invention;

FIGS. 5(a), 5(b), 5(c), 5(d) and 5(e) are views for describing theoperation of an arrangement embodying the present invention; and

FIGS. 6(a) and 6(b) are views for describing an example of using the,arrangement of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

An embodiment of a wire electrode clamping mechanism according to thepresent invention will now be described in detail with reference toFIGS. 3 through 6.

FIGS. 3(a) and 3(b) are views showing the construction of an embodimentof the present invention, in which FIG. 3(a) is a side view and FIG.3(b)is a front view. FIG. 4 is a partial, cross-sectional view showingthe detailed construction of a principal portion of the arrangement ofFIG. 3.

In the Figures, numeral 110 denotes the above-described gripper(clamping mechanism), which is constituted by a clamping member 111, apipe holder 112 having the clamping member 111 disposed on the upperportion thereof, and a wire guide pipe 113 having the upper portionthereof received in the pipe holder 112. As shown in FIG. 5(a), theclamping member 111 comprises a support wall 111a having a passage 111othrough which the wire electrode is passed, a cam body 111b whichrotates back and forth about a shaft AX, and a spring member 111c forbringing the cam body 111b into pressured contact with the support wall111a. The arrangement is such that when the cam body 111b is rotatedcounter-clockwise about the shaft AX against the force of the springmember 111c, the cam body 111b separates from the support wall 111a toopen the wire passage. As shown in FIG. 4, the wire electrode 2 ispassed through the interior of the wire guide pipe 113, the upperportion whereof is inserted into sleeves 123, 123 force-fitted into abore 112a in the pipe holder 112. Provided at a point along the pipeholder 113 is a flange 113a for limiting downward motion of the pipeholder. Provided between the flange 113a and the sleeves 123 is a spring112b for urging the wire guide pipe 113 into downward movement at alltimes and for resisting upward movement of the pipe 113 internally ofthe pipe holder 112. More specifically, though the wire guide pipe 113is capable of moving up and down in the bore 112a of the pipe holder112, downward movement thereof is limited by the flange 113a, with thelimiting action of the flange being shown in FIG. 4. Upward movement ofthe pipe compresses the spring 112b and, hence, is resisted thereby. Thepipe holder 112 is connected to the wire electrode pull-up mechanism 13of FIG. 1 and therefore moves up and down. The wire electrode pull-upmechanism 13 moves the pipe holder 112 up and down between the feedrollers 16 and the lower nozzle 11 or the upper surface of the workpiece12, as shown in FIG. 3(b). Each of the guide rollers 14 is provided on adistal end of an arm 14a, which rotates back and forth about a shaft 14cthrough an angle of approximately 90° with respect to a support portion14b. When the pipe holder 112 and wire guide pipe 113 descend, the arms14a are swung in the directions of the arrows by a mechanism, not shown,to spread the guide rollers 14, 14 apart so that the wire guide pipe113, pipe guide 112 and clamping member 111 are capable of movingbetween them. Note that a guide receiving member 114 is formed toinclude a slot 114a through which the wire guide pipe 113, pipe holder112 and clamping member 111 pass. Numeral 115 denotes a limit switch forsensing breakage of the wire electrode 2.

Let us describe the operation of the foregoing arrangement withreference to FIG. 5. The pipe 113 and cam body 111b ordinarily are inthe attitude shown in FIG. 5(a). When breakage of the wire electrode 2is sensed, the wire electrode pull-up mechanism 13 is lowered, causingthe gripper 110 (the pipe holder 112, clamping member 111 and wire guidepipe 113) to descend so that the lower end of the wire guide pipe 113supported by the pipe holder 112 passes through the workpiece and abutsagainst the upper surface of the lower nozzle 11. With further descentof the pipe holder 112, the wire guide pipe 113 is pushed up against theforce of the spring 112b (FIG. 4). As a result, the upper end of thewire guide pipe 113 engages the lower side of the cam body 111b andpushes the cam body 111b against the force of the spring member 111c sothat the cam body is rotated counter-clockwise about the shaft AX [FIG.5(b)]. This causes a clearance to be formed between the cam body 111band support wall, thereby opening the wire passage. Next, the wireelectrode feed mechanism 9, shown in FIG. 1, is operated to feed thewire electrode 2 upwardly from the lower nozzle 11. The wire electrode 2is passed through the wire guide pipe 113 and through the wire passageof the clamping member 111 until the wire electrode projects from theupper portion of the clamping member 111 [FIG. 5(c)]. The pipe holder112 is then raised by the wire electrode pull-up mechanism 13, whereuponthe wire guide pipe 113 decends relative to the pipe holder 112. Inconsequence, the cam body 111b is gradually rotated clockwise about theshaft AX owing to the baising force applied by the spring member 111cand clamps the wire electrode 2 against the support wall 111a, as shownin FIG. 5(d). It should be noted that the wire guide pipe 113 will notfall below the position shown in FIG. 5(d) by virtue of the flange 113a.When the pipe holder 112 is raised to the vicinity of the feed rollers16 by the wire electrode pull-up mechanism 13, the end of the wireelectrode 2 is inserted between the feed rollers 16 and clamped thereby.When the pipe holder 112 is raised further by the wire electrode pull-upmechanism and arrives at its uppermost position, a lever 111d of the cambody 111b abuts against an operating member 120, which is provided inthe vicinity of the feed rollers 16, whereby the cam body 111b isrotated counter-clockwise about the shaft AX to unclamp the wireelectrode 2 [FIG. 5(e)]. This makes it possible for the feed rollers 16to feed the wire electrode 2 without meeting any resistance.

Thus, the wire electrode 2 is capable of being clamped by the action ofthe wire guide pipe 113 while being guided by the wire guide pipe 113.

In the embodiment set forth above, the pipe 113 operates by passingthrough the hole in the workpiece and abutting against the nozzle 11.This is possible if the diameter of the hole 21 in the workpiece 12 islarger than that of the wire guide pipe 113, as shown in FIG. 6(a). Whenthe diameter of the hole 21 in the workpiece 12 is equal to or smallerthan that of the pipe 113, it is permissible to adopt an arrangement asshown in FIG. 6(b), wherein an adapter 125 the outer diameter whereof islarger than that of the wire guide pipe 113, is mounted on the distalend of the wire guide pipe 113 and the lower end of the adapter 115 isbrought into abutting contact with the upper surface of the workpiece12, after which the wire guide pipe 113 is operated in the mannerdescribed above.

Though the present invention has been described based on the illustratedembodiment, the invention is not limited to the illustrated embodimentbut can be modified in various ways without departing from the scope ofthe claims.

We claim:
 1. A wire electrode clamping mechanism of a wire-cut electricdischarge machine, the clamping mechanism being mounted on a wireelectrode pull-up mechanism, which pulls a wire electrode up to aposition of feed rollers disposed above a workpiece, for clamping thewire electrode delivered by a wire electrode feed mechanism disposedbelow said workpiece, the wire electrode clamping mechanism comprising:awire guide pipe for guiding said wire electrode; a pipe holder foraccommodating an upper portion of said wire guide pipe in such a mannerthat said wire guide pipe is capable of moving up and down; and aclamping member disposed on an upper portion of said pipe holder andoperated by movement of said wire guide pipe for clamping said wireelectrode.
 2. A wire electrode clamping mechanism of a wire-cut electricdischarge machine according to claim 1, wherein said clamping membercomprises a support wall having a passage through which the wireelectrode is passed, a cam member for opening and closing said passageand for clamping the wire electrode in cooperation with said supportwall, and a spring member for constantly biasing said cam member in adirection for closing said passage, said cam member being operated bysaid wire guide pipe.
 3. A wire electrode clamping mechanism of awire-cut electric discharge machine according to claim 2, wherein saidcam member has a lever which engages an operating member at an uppermostposition of said pull-up mechanism, said cam member being operatedagainst a biasing force of said spring member by engagement between saidlever and said operating member to open said passage.
 4. A wireelectrode clamping mechanism of a wire-cut electric discharge machineaccording to claim 1, wherein said wire guide pipe has a flange forengaging said pipe holder to limit downward movement of said wire guidepipe, said wire guide pipe being biased for downward movement at alltimes by a spring disposed between said flange and said pipe holder.